Process for separating strontium from fission product solution by fixing on antimonic acid



United States Patent Oflice 3,399,030 Patented Aug. 27, 1968 PROCESS FOR SEPARATING STRONTIUM FROM FISSION PRODUCT SOLUTION BY FIXING ON ANTIMONIC ACID Charles Aubertin, Bois Colombes, Jean Lefebvre, Bourgla-Reine, Gerard Galaud, Courbevoie, and Jacques Prospert, Massy, France, assignors to Commissariat a lEnergie Atomique, Paris, France No Drawing. Filed Dec. 21, 1966, Ser. No. 603,162

Claims priority, application France, Jan. 5, 1966, 44,937; Nov. 30, 1966, 85,696 5 Claims. (Cl. 23-102) ABSTRACT OF THE DISCLOSURE Strontium is obtained from acid solutions of fission products by contacting the solution with antimonic acid and eluting the strontium fixed 0n the antimonic acid with a solution containing a cation of lead or silver.

The present invention is directed to a process for separating strontium values from a complex solution. This process is primarily applicable, although not exclusively so, to the recovery of strontium-90 which is present n waste solutions of fission products derived from plants for reprocessing irradiated nuclear fuels.

The waste solutions referred-to consist of a mixture of ions in nitric acid solution. However, the process according to the invention is also applicable to any other mixture which may contain strontium in the dissolved state. The process extends, for example, to hydrochloric acid solutions. Similarly, the solution is not necessarily an acid solution but may be either a neutral or weakly basic solution inasmuch as strontium-90 precipitates above a pH of 9 approximately. The method which is proposed for recovering the strontium values contained in such solutions makes use of an exchange of ions on antimonic acid. The properties of this ion exchanger with respect to strontium have already been demonstrated. However, no satisfactory method has been proposed up to the present time for recovering strontium which is fixed on antimonic acid.

The present invention is directed to a process for separating strontium values from a complex solution and especially an acid solution of fission products, said process being essentially characterized in that it comprises contacting the solution to be processed with an ion exchanger consisting of antimonic acid and eluting the strontium values which are fixed on the antimonic acid with a solution containing a cation which has a greater afiinity for antimonic acid.

The antimonic acid which is employed as ion exchanger can be prepared according to any known method and especially by hydrolysis of antimony pentachloride; this method makes it possible to obtain products of reproducible quality.

According to a particular mode of execution of the process which forms the subject of this invention, the solution employed for displacing the strontium values which are fixed on the antimonic acid is a silver nitrate solution having a concentration within the range of 0.05 M to 1 M, and preferably 0.1 M to 0.5 M. It has been found that, by increasing the acid strength of the silver nitrate solution, the elution rate is similarly increased. It is preferable to select a nitric acid concentration which is higher than 1 N and preferably of the order of 2 N since, above this value, there is a practically negligible increase in the elution rate. However, solutions having a concentration of less than 1 N are liable to displace strontium values, the stability of silver nitrate being nevertheless better in an acid medium.

It is then possible to separate the strontium values from the eluate by one of the conventional techniques. In particular, strontium values can be precipitated in the form of carbonate or sulphate, for example, whilst the silver and the other ions remain in solution. The silver may also be separated-out by electrolysis in order to recover strontium in the dissolved state.

According to a secondary feature of the invention, the process comprises regeneration of the ion exchanger by washing with a nitric acid solution having a concentration which is higher than 2 N. The chemical strength of antimonic acid makes it possible to utilize nitric acid concentrations of at least 6 N without either degradation or loss of capacity. However, the economic optimum appears to be of the order of 5 N inasmuch as higher concentrations are not attended by any marked improvement in the regeneration factor.

Although it appears particularly advantageous to make use of nitric acid, it would also be possible without thereby departing from the scope of the invention to regenerate the ion exchanger by means of any other silver extractant. Thus, solutions of potassium thiocyanate in a nitric acid medium have been employed to elute quantitatively the silver which is fixed on antimonic acid, the concentration of silver in the eluate being constant and close to that which corresponds to the product of solubility of silver thiocyanate.

According to another mode of execution of the process according to the invention, the elution of strontium values which are fixed on antimonic acid is effected by a lead salt solution.

Either lead acetate or lead nitrate can be employed in particular as lead salt. Elution is performed, for example, by means of a lead nitrate solution having an acid strength within the range of 0 to 3 N and preferably of the order of 2 N. The lead nitrate concentration is advantageously within the range of 0.05 M to 1 M and preferably 0.1 M to 0.5 M in order to avoid any danger of precipitation.

Lead has an advantage over silver in that it is lower in cost price and its salts have higher stability. Furthermore, the regeneration of the exchanger by nitric acid is easier after elution with a lead salt than after elution with a silver salt: for a same final regeneration factor, regeneration of the exchanger can be performed with a solution having a lower acid strength and the quantity which is necessary is distinctly smaller.

There will now be described hereunder examples of execution of the process according to the invention as applied to the recovery of strontium values contained in a solution of fission products in a nitric acid medium.

Example 1 The cation which was chosen for displacing strontium values fixed on antimonic acid was silver, the aflinity of which for antimonic acid is greater than that of strontium.

of successive fixation-elution cycles are recorded in Table I below:

TABLE I Cycle 1 2 3 4 5 G 7 Fixation:

Temperature, C 60 60 60 60 60 60 ThroughputVolumes of column per hour- 0. 89 O. 82 0. 54 0. 94 0. 88 0. 92 Volume passed-Volumes of column. 61.2 57. 2 36. 2 67.3 80.2 83. 6 102. 4 Sr fixed, mgJml 2.0 2.4 1.2 1.6 1.5 1.4 1.6 Sr total, mgJml..- 2. 0 2. 6 2.1 2. 2 1. 8 1. 4 1. 6 Elution:

Tempcrature, C 20 60 60 0 90 90 90 Then 60 Then 90 Throughput--Volumes of column per hour 1.0 0.87 0.09 0. 7e 0. s0 0. 04 Volume passedVolumes of column 116. 2 45. 1 66. 0 66.0 57. 4 60. 7 62. 2 Sr eluted/Sr fixed, percent 3s. 5 6s. 0 133. 0 123. 0 117.2 90.3 100 Sr eluted/Sr total, percent 88. 5 62. 5 71.4 88. 5 100 99.3 100 The solution of processed fission products had the fol- It has been found that, when elution is performed at lowing composition: a temperature which is higher than the fixation temperatom, the exchanger exhibits a resistance to repeated cycles D and can be eluted in its entirety. Uranium 0.2 Iron 3.3 1 2 Nickel 0.8 Examp chroqnum The processed fission product solution is the same as in Alumlnum 6 Example Molybdenum Antimonic acid has the following properties: Phosphate 1n P0 0.9 Magnesium 15 Apparent density g./ml 1 S0d1\ 1m 12 Maximum capacity meq./g 5 califlum Maximum capacity in a 2 N acid medium Cerium 0.44 mach/g L0 Lanthiinum Useful capacity in an acid solution of fission prodstrorgtwpn ucts meq./g 0.05 Acid1ty 1n HNO 2 N 40 The antimonic acid which was employed as ion ex- The Charactenstlcs of the column were: ggpggg 1 gggggg g gg gigg gge Pm Hei ht m 13 Cross-sectional area cm. 0.785 Apparent density g./ml 1 Welght 10 Maximum capacity meq./g 5 Maximum capacity in a 2 N acid medium A maximum strontium fixation of 4.5 mg./g. was obmeq./g 1.0 tained with a throughput of 1 volume of column per hour Useful capacity in an acid solution of fission prodand at a temperature of 60 C.

ucts meq./g 0.05 After Washing of the column with 2 N HNO elution of Sr was performed with 0.5 M AgNO in 2 N HNO at By causing the solution of fiSSlOl'l products to percolate 60 C. Under these conditions, 90% of the fixed stronthrough a column which was loaded with antimonic acid tium were recovered. and which had the following characteristics: After regeneration of the exchanger with 6 N HNO a second fixation made it possible to fix under the same Helght H conditions a further quantity of 1.38 mg, of strontium Cross-sectional area S cm. 1.33 gram of exchamen Welght M 10 The results are recorded in Table II hereunder in D the case of three successive fixation-elution c cles and a there was obtained a strontium-fixation capacity of 2.0 fourth fixation process y mg./g. corresponding to a throughput of approximately tlug/( plume of column per hour and at ordmary tempera- TABLE H After having washed the column with HNO of 2 N Cycle 1 2 3 4 concentration, the strontium was eluted with a solution F, f of 0.1 M AgNO in 2 N HND By operating at a temperature of 60 C., it was possible to recover approxig l p r luau- 0.8 0.81 0.8 0.84 mately 90% of the strontium which was fixed. f gfigfi fjjff fffi 92.2 1&9 m4 7&2 After regeneration of the exchanger by 6 N HNO a g i q, s-i i. 58 1.38 1.11 1. 54 second fixation which was performed at 60 C. with the 7 f m same throughput made it possible to fix a further 2.6 g g g g igg o 73 0 77 0 72 of Strontlum- Vfoluime passed l i oli1:r n e s 4;) 8 1 H o c 5.5 13.7 No alteration of the exchanger became apparent during Sr g tgifi fixed, percent 89 2 92 8a 5 n the different operatlons described. Sr eluted/Sr total, percent 30.2 70.3 89.5

The results obtained during tests comprising a number Example 3 The polyantimonic acid employed had the following properties:

Apparent density g./ml 1 Maximum capacity meq./g.. 5 Maximum capacity in a 2 N acid medium meq./g 1.0

Useful capacity in an acid solution of fission products meq./g 17 If 20 ml. of liquid are processed by contacting this volume with 1 g. of exchanger, the fixation capacity at equilibrium is 17 mg. of Sr per gram of exchanger.

By way of comparison, in the case of the products of the second example, but under the same operating conditions as have been noted above, the fixation capacity is 1 mg. Sr per gram of exchanger.

Elution can be performed under the same conditions as in Example 1 or 2.

Example 4 Static tests have been performed in connection with displacements of strontium by lead.

A weight of 1 g. of antimonic acid was employed as exchanger. The antimonic acid was contacted for a period of 24 hours with 20 ml. of a fission product solution which was identical with the solution of Example 1 and fixed 0.71 mg. of strontium.

The exchanger was then reprocessed with 20 ml. of a lead nitrate solution for a period of 24 hours. The quantities of strontium which were liberated with respect to the strontium which was initially fixed are, as a function of the concentration of the elution solution employed:

12.6% for a 0.1 M lead nitrate solution 44.5% for a 0.1 M solution in 2 N HNO 91.5% for a 0.5 M lead nitrate solution 96.5% for a 0.5 M solution in 2 N HNO The regeneration of the exchanger by means of nitric acid gave the following results:

10 volumes of column of 2 N HNO regenerated the exchanger in a proportion of of its capacity;

10 additional volumes of 4 N HNO made it possible to regenerate the exchanger in a proportion of 12 additional volumes of 6 N HNO' made it possible to attain a regeneration factor of By way of comparison, if the regeneration is efiected after elution with silver nitrate, the operation must be performed in a medium which has a higher acidity and with 50 volumes of column 6 N HNO the exchanger is regenerated only up to 77%.

What we claim is:

1. A process for separating strontium values from an acid solution of fission products comprising a first step of contacting said solution with an ion exchanger consisting of antimonic acid and a second step of eluting the strontium values which are fixed on the antimonic acid with a solution containing a cation which has a greater affinity for antimonic acid than strontium, said cation being selected from the group comprising lead and silver.

2. A process according to claim 1, wherein elution is performed by means of a silver nitrate solution having an acidity within the range of 1 to 3 N and preferably of the order of 2 N.

3. A process according to claim 1, wherein elution is performed by means of a silver nitrate solution having an acid concentration within the range of 0.05 M to 1 M and preferably 0.1 M to 0.5 M.

4. A process according to claim 1, wherein elution is performed by means of a lead nitrate solution having an acid concentration within the range of 0 to 3 N and preferably of the order of 2 N.

5. A process according to claim 1, wherein elution is performed by means of a lead nitrate solution having a concentration within the range of 0.05 M to 1 M and preferably 0.1 M to 0.5 M.

References Cited UNITED STATES PATENTS 3,287,084 11/1966 Van Tuyl 252301.1 X

OTHER REFERENCES Nuclear Science Abstracts, vol. 18, No. 22; NSA- 39374; Nov. 30, 1964.

BENJAMIN R. PADGETT, Primary Examiner. S. I. LECHERT, JR., Assistant Examiner. 

